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The high abundance and environmental benignity of sulfur coupled with its high energy density of nearly 2,500 Wh kg-1 render the lithium-sulfur (Li-S) battery technology a sustainable energy storage solution for the future. Unfortunately, in Li-S batteries, the sulfur cathode suffers from poor electronic and ionic conductivity and the notorious polysulfide shuttle effect. Meanwhile, the anode suffers from continuous degradation owing to the high reactivity of Li metal. Organosulfur materials may present a way to overcome these limitations. Organic functional groups bound to sulfur could enhance electronic and ionic conductivity. Limiting the polysulfide order in an organosulfur material can minimize the shuttle effect. Furthermore, organic groups could stabilize the electrolyte-anode interface. Two studies on using organosulfur materials to overcome the challenges of Li-S will be presented. The first study shows a method to rationally design organosulfide polymers that can provide inherent Li-ion conductivity. The enhancement in ionic conductivity results in an improvement in performance under high-rate and high-loading conditions. The application of such materials in flexible Li-S batteries will be showcased. In the second study, a mechanistic understanding of how organosulfide-rich interphase at the Li-metal anode improves the stripping/plating efficiency will be elucidated. By understanding the effect of different functional groups on the efficiency of the anode, a set of design rules for developing organosulfide molecules that generate a stable interface will be proposed.

Atomically precise active sites on electrode surfaces promise new chemical transformations that simultaneously exploit both the potent physical handle of applied voltage and the highly-tailored reactivity of well-defined active sites. Often, these catalysts have off-electrode analogs in biology or organometallic chemistry, and effectively leveraging these analogies requires an understanding of how catalysis at the active site is perturbed by the complex interplay of electrolyte species and electric fields at electrode interfaces. In this work, we dissect and design two atomically precise catalysts that leverage off-electrode analogies and enable an electrochemical pathway that converts CO2 to extended carbon chains. We show that a new electrified hydroformylation reaction can be used to achieve electrochemical C-C coupling. Hydroformylation is a well-studied thermochemical reaction that performs C-C coupling by appending CO to an olefin in the presence of H2 gas. We mimic homogeneous HFN catalysts on electrode surfaces using single atom-decorated nanoparticles. We show that electrochemistry can be used to circumvent the need to supply H2 as a reactant. Instead, protons, electrons, and CO can be used to hydroformylate a model substrate. Additionally, we study the electrochemical generation of CO, a necessary reactant for hydroformylation, via immobilized cobalt phthalocyanine (CoPc) catalysts. Through collecting kinetic data over a wide range of operating conditions and quantitatively comparing candidate mechanisms, we are able to demonstrate unexpected roles of both the electrolyte and applied potential on the reaction pathway. These studies build towards a more rigorous and quantitative understanding of how the many components of an electrode interface interact with and influence catalysis on atomically precise active sites. It is crucial to carve out this complexity if we wish to effectively import catalysts or design principles from other catalytic contexts onto electrified interfaces.

The high abundance of both sulfur and sodium on earth makes room-temperature sodium-sulfur (Na-S) batteries a low-cost, environmentally benign, sustainable energy storage technology.1 High reactivity and instability of the Na-metal anode and the formation and migration of sodium polysulfides (NaPSs) at the sulfur cathode need to be mitigated to make this technology viable. The root cause of these issues can be the traced to the electrolytes that are conventionally used. To simultaneously solve the issues mentioned above, we utilize a localized high concentration electrolyte (LHCE).2 LHCE is prepared by diluting a concentrated salt solution with an inert solvent. The resulting unique solvation structure of the electrolyte favors the decomposition of the sodium salt to yield a thin, robust, ion-conducting SEI on both the anode and the cathode. This enables highly efficient and reversible stripping and plating at the Na-metal anode. At the sulfur cathode, this SEI changes the sulfur redox pathway by preventing the formation of NaPSs and steers it towards a quasi-solid-state conversion reaction. These benefits significantly prolong the life of the battery and bring the Na-S technology a step closer to viability. References A. Manthiram and X. Yu, Small, 11, 2108–2114 (2015). J. He, A. Bhargav, W. Shin, and A. Manthiram, J. Am. Chem. Soc., 143, 20241–20248 (2021). Figure 1

The Haber Bosch process has served as the dominant method of synthesizing ammonia over the last century. Ammonia produced through this route leads to a stoichiometric carbon dioxide footprint and also involves harsh conditions which limit modularity of the process. We are developing a continuous lithium-mediated approach through which nitrogen can be fixed at ambient conditions while eliminating the carbon dioxide footprint. We have elucidated the reaction network through which ammonia synthesis occurs in competition with hydrogen evolution. The coupling of kinetics and transport has a significant influence on the rates of ammonia synthesis, providing a means to improve selectivity of nitrogen fixation through non-aqueous gas diffusion electrodes.

To achieve batteries with high specific energy, long cycle life and low cost, the promising approach is to use lithium (Li) metal as anode and nickel (Ni)-rich/cobalt (Co)-less layered oxides as cathode. When the Ni content in the cathode is increased to an ultrahigh level (Ni ≥ 0.9), more specific energy can be obtained from the capacity contribution and high redox potential of Ni3+/Ni4+. Therefore, high-voltage Li metal batteries with ultrahigh-Ni layered oxide cathodes will offer a great opportunity in boosting the energy density of battery systems for applications in electrical vehicles. However, increasing Ni content intrinsically faces a dilemma between specific capacity and electrochemical cyclability for the cathode materials because of the aggressive side reactions of electrolyte on the highly reactive Ni surface. Here, we report an advanced electrolyte to enable high stability with both the reactive Li metal anode and an ultrahigh-Ni cathode LiNi0.94Co0.06O2 (NC), via the in-situ formation of a robust and conductive Li/electrolyte interphase and a protective and stable cathode/electrolyte interphase. Thus, the Li||NC cells with the advanced electrolyte can deliver a high discharge capacity of about 210 mAh g−1 and an excellent capacity retention of 81.4 % after 500 cycles at 25 °C in the voltage range of 2.8 - 4.4 V at 1C cycling rate (1.5 mA cm-2), which significantly outperform the cells using the conventional LiPF6-based electrolyte. This work provides a viable path to the successful application of ultrahigh-Ni cathode in high energy-density Li metal batteries. More detailed information will be given at the presentation.

Interdigitated Eutectic Alloy anode (IdEA) is a promising new candidate for next generation batteries due to its high specific capacity (250-300 mAh/g) [1]. Multiscale modeling approaches are essential to study such new battery chemistries. They help examine the underlying electrochemical properties and phase transitions, including the transport, kinetics and reaction schemes. In this study, we present a multiscale modeling analysis, of a Li-ion cell with a ZTB (Zn-Sn-Bi) IdEA, consisting of DFT simulation and continuum level electrochemical engineering modeling aided by experimental measurements. The DFT simulation is conducted to obtain diffusivity of the alloy anode undergoing phase changes. The electrochemical engineering model is developed based on a 1D reaction-diffusion equation and it models the kinetics and transport in the alloy anode-based battery system. Using this 1D model, a moving phase front has been observed when the eutectic alloy undergoes phase transition during charge/discharge. The cell level voltage response obtained from this model is validated with the experimental data. The practical relevance can be maximized by formulating a techno-economic model. Heligman, B.T., Kreder III, K.J. and Manthiram, A., 2019. Zn-Sn interdigitated eutectic alloy anodes with high volumetric capacity for lithium-ion batteries. Joule, 3(4), pp.1051-1063.

Significant research strides taken in the past decade have shown that lithium-sulfur (Li-S) batteries are a promising technology to compete with current Li-ion batteries owing to their significantly higher specific energy. However, some fundamental and technical challenges, such as the polysulfide shuttle effect and the need for abundant electrolyte for battery operation, have beleaguered Li-S batteries from being the next practical high-energy-density solution.[1] Recent resurgence of Li-organosulfur batteries as alternative sulfur-based cathode chemistry has shown great potential to alleviate some of these challenges.[2] These materials offer control over the order of the lithium polysulfides formed during cycling through the presence of organic terminal groups, thus minimizing the polysulfide shuttle effect. Additionally, they possess the ability to operate under lean-electrolyte conditions, a critical parameter for maximizing cell-level specific energy. This work introduces a new member into the family of organosulfur cathode materials – xanthogen polysulfides. Diisopropyl xanthogen polysulfide (DIXPS) was used as a model compound to understand the electrochemical characteristics of this new material class. Its chemical transformations within a battery will be discussed. DIXPS shows excellent long-term performance with stability up to 1,000 cycles at a high rate of 4C. DIXPS also demonstrates the ability to deliver a high specific energy of 1,313 W h kg-1 and 1,694 W h L-1 while operating under high-loading and lean-electrolyte conditions. This illustrates the practical applicability of this material. Additionally, the feasibility of using alternate anodes such as sodium-metal will also be explored. The ability to synthesize such battery materials using natural feedstocks, such as sugars and alcohols will also be examined. References: [1] A. Bhargav, J. He, A. Gupta, A. Manthiram, Joule 2020, 4, 285. [2] D. Y. Wang, W. Guo, Y. Fu, Acc. Chem. Res. 2019, 52, 2290. Figure 1

Lithium-ion batteries have become an integral part of our daily life, powering portable electronic devices. They are in the process of transforming the transportation sector through electrification. They are also being intensively pursued for grid storage of electricity produced from renewable sources. Cost, sustainability, and supply-chain issues are major considerations in employing lithium-ion batteries for electric vehicle (EV) and grid storage applications. In the case of EVs, energy density or driving distance between charges is a critical parameter as well. These considerations have created immense interest to reduce cobalt content or eliminate cobalt altogether in layered oxide cathodes. With this perspective, the research and development trend has been to increase the nickel content and lower the cobalt content in LiNi1-y-xMny-CozO2 (NMC) cathodes. For instance, the industry has been gradually moving from LiCoO2 with 100% Co to NMC-111 with 33% Ni and 33% Co to NMC-622 with 60% Ni and 20% Co to NMC-811 with 80% Ni and 10% Co. While the increase in Ni content offers both an increase in capacity and a reduction in cost, it is also met with serious technical challenges. As the Ni content increases beyond 60%, the cathodes suffer from poor cycle, thermal, and air stabilities. The problems become exponentially challenging as the Ni content increases. This presentation will focus on improving the cycle, thermal, and air stabilities through compositional and controlled synthesis approaches, while reducing the Co content significantly as well as eliminating it altogether to give low- and zero-cobalt layered oxide cathodes with high capacities. The low- and zero-cobalt layered oxide cathodes are synthesized by a coprecipitation of the hydroxide precursors with appropriate doping, employing a tank reactor, followed by calcining with lithium hydroxide at optimal temperatures under a flowing oxygen atmosphere. As the Ni content increases, the calcining temperature and conditions need to be sensitively controlled to obtain high-quality samples. The presentation will particularly focus on the performance evaluation and a fundamental understanding of the degradation mechanisms with cathodes containing > 90% nickel, including LiNiO2. The electrochemical performances are evaluated with full pouch cells by pairing the cathodes with graphite anode. The bulk and surface instabilities are assessed by employing a suite of advanced analytical methodologies, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), time-of-flight – secondary ion mass spectrometry (TOF-SIMS), high-resolution transmission electron microscopy (HR-TEM), etc. before and after extended cycling of full pouch cells. The presentation will also focus on assessing and improving the air stability as well as thermal stability of various compositions. Approaches to realize capacity values as high as 220 mAh/g will be presented.

Oxygen-atom functionalization of chemical intermediates is critical for the production of diverse textiles, plastics, and pharmaceuticals, including epoxides and ketones. The wet chemical and thermochemical routes used today suffer from large carbon dioxide footprints, stoichiometric waste products, and hazardous reagents. We have developed a route whereby water can be used as the oxygen atom source in functionalization reactions of hydrocarbons. At the cathode, hydrogen is selectively generated. Overall, this reaction provides a means by which the oxidizing equivalents can go towards generating a valuable product rather than generating oxygen which is simply vented in a conventional water electrolyzer. We have developed mechanistic understanding of how water is oxidized, providing means by which the selectivity for oxygen-atom functionalization can be rationally improved.

The lithium-ion battery technology is based on intercalation chemistry phenomenon. The 2019 Chemistry Nobel Laurette Stanley Whittingham was the first to show in 1976 how the intercalation phenomenon can be utilized to realize a rechargeable lithium battery. He demonstrated the concept with a lithium-metal anode and a layered titanium sulfide cathode. Since then the field of intercalation chemistry for electrical energy storage has evolved during the past four decades, encompassing a variety of materials and intercalation working ions, such as monovalent lithium, sodium, and potassium, divalent magnesium, calcium, and zinc, and trivalent aluminum ions. Among the intercalation materials, oxides are at the forefront with rich fundamental structural chemistry and electrochemistry as well as with profound technological and societal impact. Accordingly, this presentation will focus on the richness and complexities of the intercalation chemistry of transition-metal oxides. The scientific and technological impact of the intercalation chemistry of oxides is illustrated by the three families of cathodes for practical lithium-ion batteries: layered oxides, spinel oxides, and polyanion oxides. The presentation will first provide a comparison of these three families of oxides, pointing out the pros and cons with respect to employing them as electrodes in rechargeable batteries as well as their limiting features from a fundamental solid-state chemistry point of view. Particularly, the structural and chemical features that impact the charge-storage capacity, operating voltage, rate capability, and practical energy density will be discussed. As we move forward, the layered oxide cathodes have become the prime candidates from an energy density consideration point of view, particularly for portable electronics and electric vehicles. However, bulk and surface instabilities during charge-discharge limit their practical energy density and cycle life, while the use of significant amounts of cobalt in them poses concerns on sustainability, cost, and supply-chain issues. Therefore, the presentation will then focus on layered oxide cathodes with high nickel contents and very low or no cobalt content to increase the energy density and lower the cost. Particularly, the role of modifications in chemical compositions through cationic substitutions on the cycle, thermal, and air instabilities will be discussed from a fundamental solid-state chemistry point of view. The use of advanced analytical techniques, such as in-situ x-ray diffraction, x-ray photoelectron spectroscopy, time of flight secondary ion mass spectrometry, scanning electron microscopy, high-resolution transmission electron microscopy, and differential scanning calorimetry in understanding the intricacies of the cathodes and mitigating the problems will be presented.

The practical realization of lithium-sulfur (Li-S) batteries with high energy density is currently limited by the poor cyclability of the lithium-metal anode. Lithium plating and stripping in the liquid ether-based electrolyte is irreversible over long-term cycling and this leads to rapid capacity fade. Due to the reducing nature of lithium, parasitic side reactions with the electrolyte also occur with considerable severity during cell operation. This eliminates a significant portion of the available lithium inventory and electrolyte supply, and the cell fails prematurely. These problems can be sidestepped by employing surplus lithium and electrolyte in the cell, but this compromises the stack-level energy density. Stabilizing lithium deposition and reducing electrolyte decomposition is of critical importance to enabling commercially viable Li-S batteries with high energy density and long cycle life. The chemistry of Li-S batteries is unique due to the generation of polysulfide intermediates at the cathode that are soluble in the electrolyte. The polysulfides migrate to the anode side, which fundamentally alters its interfacial chemistry by forming reduced sulfide species (Li2S/Li2S2) on the lithium surface. These species are known to have an intrinsically stabilizing effect on lithium deposition, although it is not sufficient to enable stable operation of Li-S batteries at reasonable current densities. Nevertheless, the modification of electrolyte-soluble polysulfide species offers a unique opportunity for tuning the interfacial chemistry of the lithium-metal anode towards stabilizing lithium deposition and reducing electrolyte decomposition. Tellurium, which sits two position below sulfur in Group 16 of the periodic table, is an excellent candidate element for modifying the composition of polysulfide intermediates in Li-S batteries and forming potentially favorable components in the lithium SEI layer. It was found that elemental tellurium (Te0) could be facilely assimilated into polysulfide species to form soluble mixed polytellurosulfide species when left in an ethereal solution of Li2S6. This was confirmed by the characteristic isotopic signature of tellurium using mass spectrometry. The polytellurosulfide species were found to reduce on the surface of lithium metal to form red-colored lithium thiotellurate (Li2TeS3), which was confirmed by X-ray techniques. In contrast to Li2S, Li2TeS3 is expected to be a significantly better ionic conductor due to the reduced electron density around the sulfur atoms. This would help engender a uniform lithium-ion flux on the lithium surface, enabling homogenous lithium deposition. Based on the results above, elemental tellurium was simply added in a 1 : 10 molar ratio to the sulfur/Li2S cathode to modify the chemistry of Li-S batteries. During cell operation, the generated polysulfides (Li2Sn) reacted with the Te0 additive in the cathode to form polytellurosulfide (Li2TexSy) species in-situ. The crossover of these tellurium-containing species to the anode side was confirmed by the detection of a significant amount of Li2TeS3 on the lithium surface. The favorable properties of Li2TeS3 as a lithium SEI component enabled the formation of dense and uniform lithium deposits and significantly improved lithium cycling efficiency. In the anode-free full cell configuration, which pairs a Li2S cathode with a bare anode current collector and contains zero excess lithium (N/P ratio = 1), the addition of tellurium improved cycle life by a factor of 7. The loss of the limited lithium inventory in the anode-free cell was reduced from 2% per cycle to 0.25% per cycle. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealed the drastically reduced electrolyte decomposition on lithium surface due to tellurium-stabilized lithium deposition. The reduced electrolyte decomposition could allow a limited electrolyte supply to be retained for a longer number of cycles, thus enabling extended cyclability under lean-electrolyte conditions. This was confirmed using large-area pouch cells employing a high-loading sulfur cathode (5.2 mg cm-2), a lithium-foil anode, and a low electrolyte/sulfur (E/S) ratio of 4.5 µl mg-1. Under such stringent cell design conditions, the pouch cells could be cycled stably for nearly 100 cycles with the addition of tellurium. In contrast, the control cell failed within 25 cycles. This work demonstrates a novel, effective, and robust strategy of adding tellurium to the sulfur/Li2S cathode for stabilizing lithium deposition and reducing electrolyte decomposition in Li-S batteries. This improves cycle life in energy-dense cell configurations operating with a limited lithium inventory or electrolyte supply. Importantly, this approach is scalable as no expensive or complicated pre-treatments or coatings of the lithium-metal anode are necessary. The unique chemistry of tellurium in the polysulfide-rich environment of Li-S batteries opens a new frontier in research in Li-S batteries, bringing them one step closer to reality. Figure 1

Lactones serve as key synthetic intermediates for the large-scale production of several important chemicals, such as polymers, pharmaceuticals, and scents. Current thermochemical methods for the formation of some lactones rely on molecular oxidants, which yield stoichiometric side products that result in a poor atom economy and impose safety hazards when in contact with organic substrates and solvents. Electrochemical synthesis can alleviate these concerns by exploiting an applied potential to enable the possibility of a clean and safe route for lactonization. In this study, we investigated the mechanism of electrochemical lactone formation from cyclic ketones. When using a platinum anode and cathode in acetonitrile with 10 M H2O and 400 mM cyclohexanone, we found that non-Baeyer-Villiger products, δ-hexanolactone and ɣ-caprolactone, are formed with a total Faradaic efficiency of ~20%. Isotope labeling experiments support that water is the oxygen atom source for this reaction. In addition, electrochemical kinetic data suggest a 1st order dependence on water at low water concentrations (2O) and a 0th order dependence on the substrate, cyclohexanone. A Tafel slope of 139 mV/decade was measured at 400 mM cyclohexanone and 10 M H2O, implying an initial electron transfer as the rate determining step. Literature proposed mechanisms for similar transformations suggest an outer sphere pathway. However, based on the collected electrochemical kinetic data, we propose the possibility that Pt reacts with water in an initial electron transfer that forms Pt-OH, which can subsequently react with the ketone substrate. A subsequent electron transfer forms a ring opened carboxylic acid cation that can reclose to form either of the observed five- or six-member ring lactone products.

The lithium-sulfur (Li-S) chemistry holds tremendous potential for realizing the next generation of rechargeable batteries with high energy density and low cost. Despite its promise, the practical development of Li-S batteries is hindered by its limited cyclability, which is mainly caused by the poor plating and stripping efficiency of the lithium-metal anode. In liquid electrolytes, lithium deposits adopt a mossy dendritic filamentous morphology with high surface area. Due to the reactive nature of lithium, the electrolyte irreversibly decomposes on the lithium surface, which consumes both the lithium and electrolyte supply in the cell. However, significant questions remain about the mechanisms that underlie lithium inventory loss and the role of the lithium-electrolyte interface. Further commercial adoption of Li-S batteries is conditional on developing an effective strategy for improving the reversibility of lithium deposition, which is in turn dependent on developing a clear mechanistic understanding of lithium degradation with cycling. In this study, we use the anode-free full cell configuration, which pairs a Li2S cathode with a bare nickel foil as the anode current collector. Since there is no excess lithium in the system (N/P ratio = 1), the cyclability of anode-free full cells depends on the electrochemically accessible lithium inventory in the system. By identifying the sulfur-limited and lithium-limited regimes in the cycling of anode-free full cells, the lithium inventory loss rate per cycle (LILR) can be quantitatively estimated. This parameter provides an effective, robust, and quantifiable description of lithium degradation with cycling in cells with a limited lithium inventory. Lithium degradation displays a strong dependence on the applied current density, with the LILR increasing from 0.6% per cycle to 1.8% per cycle when the current rate is increased from C/10 to C/5. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was applied to analyze the chemical composition of the deposited lithium in the anode-free full cells with different cycle numbers. The integrated intensity for Li2 -, which is indicative of metallic lithium, was found to show negligible variation with cycle number. In contrast, the electrochemically accessible lithium inventory is known to show a clear decrease with cycling. Thus, there is poor correlation between the lithium inventory available with cycle number and the amount of metallic lithium detected with ToF-SIMS. This indicates that lithium inventory depletion in Li-S batteries is not just due to the loss of lithium in parasitic side reactions with the electrolyte to form lithium SEI compounds (Li+), but largely due to the formation of electrochemically inaccessible “dead” metallic lithium. Further analysis with ToF-SIMS revealed the growth of a thick layer of electrolyte decomposition products on the surface of the deposited lithium. Since the decomposition products are expected to be ionically insulating, lithium-ion access to and from the metallic lithium underneath is blocked, which renders it electrochemically inaccessible or “dead”. The bulk of the deposited lithium is found to be composed of fully reduced decomposition products, such as Li2O, Li2S, LiH, and LiOH. In particular, the hydrogen-containing decomposition products such as LiH and LiOH are found to show a sharp decrease in concentration with cycling. This is attributed to the substantial gas evolution that occurs at the lithium anode during cell operation. These gases include H2, CH4, and C2H4, and their generation is correlated with the loss of lithium inventory with cycling. This could play an additional role in limiting electrochemical accessibility to the trapped metallic lithium by blocking off ionic and electronic conduction pathways, especially if the gases themselves are trapped in void spaces of the porous lithium deposit. This work illuminates the mechanisms that underlie the loss of lithium inventory in Li-S batteries by a careful application of the anode-free full cell configuration and analytical tools, such as ToF-SIMS. The role of the devolving lithium-electrolyte interface in engendering lithium degradation with cycling is clarified. The framework demonstrated in this work and the conclusions drawn are applicable not just to Li-S batteries, but to lithium-metal-based batteries in general. It is hoped that the insights generated in this work can motivate efforts towards enabling stable operation of lithium-metal anodes and long cycle life for energy-dense Li-S batteries. Figure 1